The present disclosure relates in general to a battery charging apparatus and method, in particular, but not by way of limitation, for a plurality of Lithium Sulfur (LiS) battery cells.
LiS rechargeable batteries provide users with high-energy and light-weight solutions. For example, LiS batteries developed by Sion Power™ Corporation, Tucson Ariz. are reported to be capable of delivering a specific energy of 400 Wh/kg and an energy density of 425 Wh/liter. The specific energy of the LiS battery exceeds that of state-of-the-art Lithium Ion chemistry by a factor of greater than two, while the energy density stands at an equivalent level. That is, a LiS battery provides the same runtime for a portable computer in less than half the weight, or twice the runtime in the same weight while having a volume comparable to a Lithium Ion battery. Another reported advantage of LiS batteries is their ability to work well in very cold weather. Typical applications include unmanned aerial vehicles, military communication systems, rugged notebook computers, tablet personal computers, and portable medical devices.
In a battery charging process, sufficient charge at an appropriate rate is supplied so that the battery can deliver its rated capacity. Overcharge can cause permanent damage to batteries. Even when the degree of overcharge is not so severe, the battery could become unusable well before its expected lifetime has expired. Furthermore, most batteries generate heat as they charge; for some type of batteries, excessive charge can pose a potential fire risk. Conventional heat management involves heat sinking by using, for example, circuit boards with large copper areas, thereby increasing the cost.
When charging a plurality of batteries, the charge capacities of the pack as a whole can be limited by the characteristics of one of its batteries. The first battery to reach charge complete could prevent the others from being charged, for example. Therefore, in general, the optimal battery pack includes “balanced” batteries with nearly the same capacity and state of charge. For this reason, battery packs should be assembled using cells from the same supplier and production lot. Even with that precaution, due to unavoidable variations in chemistry from battery to battery, abnormal conditions could arise from one particular battery in a battery pack.
In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.